A query execution plan is an ordered set of steps used to access data in a database system. The query execution plan defines in detail, for example, which steps will be performed in order to process a query (a request for information retrieval) and in what order the steps will be performed. Optimal execution time is a crucial aspect of query performance, but the complexity of its calculation can make the preparation of a query execution plan difficult, especially when online analytical processing (OLAP) environments are considered.